Water Hammer

Discussion in 'Irrigation' started by Green Sweep, Sep 16, 2004.

  1. Green Sweep

    Green Sweep LawnSite Senior Member
    Posts: 321

    I have a system that we installed 3 years ago that has been experiencing teribble water hammer all summer. The system never did this before. There is a 3/4" copper main line that is T'd inside the house & exits the front & back. There are 2 master valves feeding 1" mainlines which feed 12 zones with 1" laterals (all PVC). All valves & heads are Rain Bird & the system runs @ 100psi. We have already: Replaced both master valve diaphragms, installed 2 water hammer reducers on the copper inside. Neither of these did a damn thing to stop the water hammer. My next 2 options are: Replace all diaphagms (but why? the system is only 3 years old!), Or add SAM fittings to every head to prevent the water from draining. Has anyone out there had similar problems? If so, I'd appreciate your input. This lady has been a saint (I would have been really ticked). She has a newborn baby & has had to listen to an AK-47 in her basement every other day at 6:30 in the morning.
     
  2. DanaMac

    DanaMac LawnSite Fanatic
    Posts: 13,156

    100 psi seems high but if that is the way you designed it for installation, lowering it may affect performance. You could try it though. Put in a PRV (pressure regulating valve) and reduce it to 80 or 90 psi and see if that helps and also allows the zones to function properly.

    You also mentioned the valves are Rainbird. I have had many problems with Rainbird DV-100 valves shutting off very fast and creating water hammer when they shut off. I have seen manifolds blow apart due to it, even at 60-70 psi. So I no longer use DV valves. One thing that seemed to help though, is swapping out the top of the valves to make them a flow control top, and then reducing the flow slightly. I have had that work sometimes and not on others. Are the DVs rated for 100 psi? Don't have my specs in front of me.

    You might also take apart the PVB or RP and see if anything is damaged inside(check valve) that could be disrupting things. Hope you get it, I hate those nagging ongoing problem jobs.
     
  3. jerryrwm

    jerryrwm LawnSite Bronze Member
    Posts: 1,274

    The "design" pressure sounds excessively high. Which means that the static pressure must be high also. House sitting at the bottom of a steep hill?

    The equipment you are using is fine. The DV valves are rated for 150 psi as are just about every plastic valve on the market. They will as DM said, create water hammer, but so does every valve on the market. The closing time on any valve is mainly dependent on the velocity of water, which is affected by the pressure pushing it. Lower the pressure, slow the water, reduce the water hammer. Good solid cement welds on the fittings reduces manifold blow-outs.

    Changing out heads to SAMS will not solve the problem. Sprinkler heads are their own water hammer arrestors. The water hammer problems you are experiencing is between the zone valves and the master valves, and between the master valves and city main.

    Sounds like the whole house could use a pressure regulating valve before it enters the house. Set at under 75 psi. Can't think of too many reasons why a residential irrigation system would need to be design for over 60-70 psi.

    Also, you may not have sized your water hammer arrestors properly, or you need more. Check manufacturer's spec on the flow/pressure that they are rated for. You may need to add several more along the line.

    Jerry
     
  4. DanaMac

    DanaMac LawnSite Fanatic
    Posts: 13,156

    Jerry - I know what your saying, but I have also taken care of the problem by replacing DV valves with other valves - Irritrol or Hunter. I don't see those valves shuting down as fast, causing that hammer problem. They tend to shut down "softer". Maybe not slower.
     
  5. Green Sweep

    Green Sweep LawnSite Senior Member
    Posts: 321

    Thank you guys for the input, that was exactly what I was looking for. To address the psi issue, most of our systems run on 60 - 70 psi. We do have a few at 100 psi or more & we roll with it. We were thinking of adding a PRV as a last resort. The system runs beautifully now & really did not want to altar that. However, I think that only minor nozzle adjustments would be needed. Jerry, the house sits on top of a hill & I got the SAMS idea because the hammer seems to be loudest on zones along the street at the bottom. I theorized that the water rushing down the hill at that velocity was causing the pipes to really shake. But, if that were the case, the water hammer would not have taken 3 years to start. Also, the pipes are shaking when the valves are opening, not closing. I know this because I ran the system with a 10 second delay between zones while standing at the meter. My last question is why 3 years? If too much pressure is the issue, then why did it take 3 years to start water hammering?
     
  6. I feel your pain..many times I have asked the question "why?"

    At 100psi are your nozzles fogging excessively? I would think they would be...not optimum by any stretch. If it works well at 100psi, I'm guessing it will work even better at 60...unless of course the system wasn't designed properly and you need 100 psi to get the coverage you need.

    Which seems a bit funny to me...I don't think heads work better or throw farther at 100psi...they may appear to..but I bet they fog more than they should.

    Good luck
     
  7. Critical Care

    Critical Care LawnSite Bronze Member
    Posts: 1,654

    I've been using Hunter HPV valves that close slowly to supress water hammer. I wonder if they could solve your problem. I'm a bit curious as to how much water, gpm, you have flowing through the 3/4" copper and into the 1" mains?

    Had a slight hammer problem with a large 2" Irritrol "normally open" master valve designed to shut off a field irrigation system whenever the house irrigation was turned on. From reviewing the flow rate specs on the 2" valve I feel that I could have gotten away from the water hammer (perhaps) by downsizing the valve to 1 1/2".
     
  8. MikeK

    MikeK LawnSite Member
    Posts: 145

    Since water hammer is a function of pressure, it's my guess that the high static water pressures are causing the problem. Could it be that the water pressure in your area increased in your area since the system was installed?
    Install a pressure regulator and while you are at it, do it in such a way that it regulates your domestic water supply as well as the sprinkler system.
    I am guessing that toilet and faucet vlaves do not live to long exposed to 100 PSI.
     
  9. jerryrwm

    jerryrwm LawnSite Bronze Member
    Posts: 1,274

    I gotta agree with MikeK. The static pressure is extremely high and that diaphragm is fluttering it's a$$ off to open creating the hammer vibrations. I would also guess that the faucets in the house will almost take the glass out of your hand when you open them. And that commode tank probably gets filled pretty quickly too!

    I still would recommend a PRV on the service line. Hell they are only about $65.00 for a 1" and time to put it in is minimal.

    As for the three year period before it showed up as a problem. What has changed in the area? More houses or added subdivision that might have put in newer distribution lines to the area replacing older and smaller lines. Or maybe the utility district added a pump station or two, or upgraded their pumps? Usually something that happens after a long period of time is more externally caused.

    Hope you get it sorted out.

    Jerry
     
  10. Green Sweep

    Green Sweep LawnSite Senior Member
    Posts: 321

    Our plumber is scheduled to install a PRV next week. Will keep you posted.
     

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